The distal radioulnar joint (DRUJ) is an essential portion of the wrist that allows rotation or supination and pronation of the forearm. With reference to FIG. 1, the dorsal side of the bone structure of a patient's left proximal metacarpals 4 and carpals 6 is illustrated in conjunction with the radius 8 and the ulna 10. The radius 8 articulates in pronation and supination on the distal head of the ulna 10 at the sigmoid notch 12. The ulna 10, a slightly bowed bone linked to the wrist, translates dorsal-palmarly to accept the modestly bowed radius 8. Since the sigmoid notch 12 in most wrists is relatively flat, ligaments are required to support the distal ulna and the triangular fibrocartilage (TFC) discus 14, located where the ulna meets the wrist. Ligaments supporting the TFC include radioulnar ligaments (RULs) and ulnocarpal ligaments (UCLs). Together with the TFC, these ligaments form the triangular fibrocartilage complex (TFCC) 16, as depicted simplistically in FIG. 1. Additional support of the DRUJ is mediated by the interosseous membrane 9, a fibrous sheet connecting the radius 8 and the ulna 10. The DRUJ 18 can be thought of as having three degrees of motion: translation in the distal-proximal plane, rotation around the distal-proximal plane, and translation in the dorsal-palmar plane.
The movement and rotation of these bones enabled by support from the ligaments allows humans to open doors, turn screwdrivers, and many other common daily activities, Like any other joint in the body, the DUI can become significantly damaged through traumatic or degenerative destruction. Pain and dysfunction often follows any biomechanical disruption and patients eventually become debilitated and seek medical attention. Historically, this problem was treated with removing half of the joint and not restoring any anatomical structure, limiting the range of motion. In recent years however, implants have been designed to reconstruct the DRUJ.
The current prosthetic implants only allow two of the three degrees of motion: translation along the distal-proximal plane and rotation around the distal-proximal plane, but neither allow translation along the dorsal-palmar plane. Additionally, the current implants do not have the correct amount of constraint in their designs or require extremely precise alignment in order to provide proper motion. The ulnar stem is slightly bowed which has not been respected in current implant designs as all ulnar stem components are straight. This causes problems with insertion of the prosthetic implant as well as fixation and therefore long-term survival and loosening. Accordingly, there remains a need in the art for an improved DRUJ implant system that provides the stability and ranges of motion that mimic the healthy wrist.